Little is known about the effects of heavy metal ions on the early development of mammalian embryos. The overall objective of the proposed research is to examine the effects of 24 different heavy metals, applied either in vivo or in vitro, on the development of early mouse embryos. The following subjects will be studied: 1. The development in vitro of mouse 1-cell and 2-cell embryos in the presence of various concentrations of particular metal ions. Fractions of blastocysts developed from cultured embryos will be estimated and karyological analysis of embryos performed. 2. Postimplantation development of blastocysts obtained from 1- or 2-cell embryos grown in vitro in the presence of a studied heavy metal, and then transferred to foster mothers; development of blastocysts exposed for 12-24 hrs to a given metal. Numbers of implantation and resorption sites, of normal and abnormal fetuses, and the size and survival of litters will be assayed. 3. The effects of intravaginal deposition of heavy metal salts on the preimplantation and postimplantation development of mouse embryos. Assayed mainly as in point 2. 4. The effects of heavy metals provided in the diet of mothers shortly before fertilization and during preimplantation development of embryos on preimplantation and postimplantation development of embryos. Assayed mainly as in point 2.